In a power or main circuit breaker system within an electric distribution system, a main circuit breaker or power circuit breaker is connected between a power source terminal and a plurality of branch load circuits. Additionally, feeder circuits may be coupled in the electrical distribution system. Typically, each branch or feeder circuit is protected by a circuit breaker or fuse connected between the power source and the load, such as an induction motor or the like. In operation, the main circuit breaker typically is configured to operate, or trip at a higher power setting, current pass through, then the branch circuit breakers or feeder circuit breakers. If a short circuit or other reason to cut power to a specific load circuit occurs, the feeder or branch circuit breaker is configured to open before the time delay designed into the main circuit breaker. In such operation, only the affected load is cut from the electrical distribution system with the remaining load circuits continuing to be connected to the electrical distribution system.
In the event that personnel, a human being, has to enter the area where a short circuit or work on an electrical machine is needed, there is a possibility of arc flash from the surrounding “live” circuitry. An arc flash hazard, as defined by the standard for electrical safety requirements for employee workplaces (NFPA70E-2000) defines arc flash hazard as “a dangerous condition associated with the release of energy caused by an electrical arc”. An electrical arc operates at temperatures of several thousand degrees Celsius and creates a pressure wave, not unlike an explosion, causing metal particles, equipment parts and other loose items to be expelled from the electrical arc flash area in addition to the expulsion of hot, ionized gases. If a human being is in the vicinity of such arc flash hazard, bodily injury, including death can result. Federal regulations, as well as the National Electric Code, specifies warnings, markings, and personnel protection equipment, clothing, goggles, gloves, etc., that are designed to protect personnel working in such flash areas.
In addition to the warnings, discussed above, the setting of boundaries that mark where personnel could not enter without wearing appropriate protective gear/clothing is used to designate the arc flash hazard area. Before personnel could approach electrical gear within such designated flash protection boundary, the personnel would be required to wear fire-retardant arc flash suits which are hot, expensive and limit the personnel's ability to work on the electrical equipment. Another alternative available to working in the arc flash hazard protected area is to open the main circuit breaker which would cut power to all of the branch and feeder circuits protected by such main circuit breaker. Such procedure is expensive and inefficient.
Thus, there is needed a method of a main circuit breaker system operation using a trip unit that is capable of being programmed to operate in response to a first set of parameters or a second set of parameters corresponding to a condition relating to the main circuit breaker system, such as the presence of a human being within a designated area. There is further need for a method of reducing arc flash in a main circuit breaker system when a human being enters a predetermined flash protection boundary. There is an additional need for an occupancy-based control device coupled to a trip unit of the main circuit breaker that can change the instantaneous and short time protective settings of the circuit in response to a predetermined set of conditions.